Eelgrass Ecosystems Research Articles

Mapping and Characterizing Eelgrass Meadows Using UAV Imagery in Placentia Bay and Trinity Bay, Newfoundland and Labrador, Canada

Sustainable coastal social–ecological systems rely on healthy ecosystems known to provide benefits to both nature and people. A key ecosystem found globally is seagrass, for which maps at a scale relevant to inform conservation and management efforts are often missing. Eelgrass (Zostera marina), a species of seagrass found throughout the northern hemisphere, has been declining in Placentia Bay, an ecologically and biologically significant area of Canada’s east coast subject to an increasing human impact. This research provides baseline information on the distribution of eelgrass meadows and their anthropogenic stressors at seven sites of Placentia Bay and three sites of the adjacent Trinity Bay, on the island of Newfoundland. High-resolution maps of eelgrass meadows were created by combining ground-truth underwater videos with unmanned aerial vehicle imagery classified with an object-based image analysis approach. Visual analyses of the imagery and underwater videos were conducted to characterize sites based on the presence of physical disturbances and the semi-quantitative cover of epiphytes, an indication of nutrient enrichment. A total eelgrass area of ~1 km2 was mapped across the 10 sites, with an overall map accuracy of over 80% for 8 of the 10 sites. Results indicated minimum pressures of physical disturbance and eutrophication affecting eelgrass in the region, likely due to the small population size of the communities near the eelgrass meadows. These baseline data will promote the sustainability of potential future coastal development in the region by facilitating the future monitoring and conservation of eelgrass ecosystems.

Temperature threshold for seagrass (Zostera marina) ecosystem production derived from in situ aquatic eddy covariance measurements

As seagrass meadows are increasingly threatened by warming oceans and extreme heating events, it is critical that we enhance our understanding of their ecosystem response to heat stress. This study relied on our extensive database of hourly eelgrass Zostera marina ecosystem metabolism to determine, for the first time, the temperature stress threshold (Tth) of Z. marina meadows under naturally varying in situ conditions. Eelgrass ecosystem metabolism was measured using the aquatic eddy covariance technique in a 20 km2 meadow at the Virginia Coast Reserve (USA). We constructed and fitted a non-linear multivariate model to identify 28.6°C as the threshold above which substantial negative effects on net photosynthesis occur. On average, daytime oxygen fluxes decreased by 50% on afternoons when Tth was exceeded, which shifted daily net ecosystem metabolism from metabolic balance to net heterotrophy and therefore a loss in carbon. This study highlights the vulnerability of eelgrass meadows to future warming projections.

The linkage between spatial and temporal variations in epifaunal and primary producer communities in eelgrass (Zostera marina) beds

Environmental variability within estuaries and lagoons creates environmental gradients. Spatial variations in environments associated with environmental gradients shape spatial variations in primary producer and invertebrate communities. However, whether larger spatial variations are linked to greater temporal variations in the communities remained unclear. To understand the linkage between spatial and temporal variations in the communities and the factors shaping these variations, we targeted various functional groups of primary producers and invertebrates (epifauna) in eelgrass (Zostera marina) ecosystems in lagoons with and without distinct salinity gradients. We tested the following hypotheses: 1) larger spatial variation in the primary producer biomasses and epifaunal community structures (abundance, biomass, and species richness) are associated with greater temporal variation in the structures, and 2) salinity would be a more pronounced factor than water temperature and biomasses of primary producers in shaping the community structures in the lagoon with a salinity gradient. Our results showed that temporal and spatial variations in the primary producer biomasses and community structures of epifauna were larger in the lagoon with a salinity gradient. Moreover, salinity, water temperature, and the biomasses of primary producers affected the spatio-temporal variations in the community structures of epifauna, regardless of the presence of the gradients. We present from these results the connection between spatial and temporal variations of the primary producer and epifaunal community structures and the effects of abiotic and biotic factors shaping the communities.

Coastal community perceptions of eelgrass in Atlantic Canada: Considerations for management

Societal awareness of the value of coastal ecosystems and the services they provide is necessary for public support of conservation and management decisions, yet public perception is seldom explored. We present findings from an online survey on coastal community perceptions of eelgrass (Zostera marina) and its management in Atlantic Canada and compare these findings with related scientific literature. Responses from 114 participants in an anonymous online survey indicate that people residing in coastal communities in Atlantic Canada are aware of the status of eelgrass meadows in their region, the services they provide, and threats to eelgrass meadows. Consistent with scientific literature, participants identified fish habitat (97%), coastal protection (93%), and water quality maintenance (89%) as the three most important eelgrass ecosystem services. Only 51% of participants selected climate change mitigation as a valuable eelgrass ecosystem service, consistent with its more recent appearance in scientific publications and the absence of Canadian policies on this service. Coastal development, climate change, and invasive species were identified as the most likely causes of change in eelgrass. More than 80% of participants indicated a need for increased restoration and protection, and 76% agreed that the public should be more involved in all aspects of eelgrass management. Although based on a non-random sample of the population, this study illustrates a relationship between scientific knowledge, public awareness, and existing Canadian policies. Participants’ knowledge of the societal benefits of eelgrass meadows and support for and interest in participating in the management process signals an opportunity to expand public engagement with eelgrass conservation efforts. This could begin by refining and introducing policies that protect the numerous ecosystem services eelgrass meadows provide.

Unoccupied aerial vehicle-assisted monitoring of benthic vegetation in the coastal zone enhances the quality of ecological data

Traditional monitoring (e.g., in-water based surveys) of eelgrass meadows and perennial macroalgae in coastal areas is time and labor intensive, requires extensive equipment, and the collected data has a low temporal resolution. Further, divers and Remotely Operated Vehicles (ROVs) have a low spatial extent that cover small fractions of full systems. The inherent heterogeneity of eelgrass meadows and macroalgae assemblages in these coastal systems makes interpolation and extrapolation of observations complicated and, as such, methods to collect data on larger spatial scales whilst retaining high spatial resolution is required to guide management. Recently, the utilization of Unoccupied Aerial Vehicles (UAVs) has gained popularity in ecological sciences due to their ability to rapidly collect large amounts of area-based and georeferenced data, making it possible to monitor the spatial extent and status of SAV communities with limited equipment requirements compared to ROVs or diver surveys. This paper is focused on the increased value provided by UAV-based, data collection (visual/Red Green Blue imagery) and Object Based Image Analysis for gaining an improved understanding of eelgrass recovery. It is demonstrated that delineation and classification of two species of SAV ( Fucus vesiculosus and Zostera marina) is possible; with an error matrix indicating 86–92% accuracy. Classified maps also highlighted the increasing biomass and areal coverage of F. vesiculosus as a potential stressor to eelgrass meadows. Further, authors derive a statistically significant conversion of percentage cover to biomass ( R2 = 0.96 for Fucus vesiculosus, R2 = 0.89 for Zostera marina total biomass, and R2 = 0.94 for AGB alone, p < 0.001). Results here provide an example of mapping cover and biomass of SAV and provide a tool to undertake spatio-temporal analyses to enhance the understanding of eelgrass ecosystem dynamics.

Physical disturbance by recovering sea otter populations increases eelgrass genetic diversity.

Most knowledge regarding the role of predators is ecological in nature. Here, we report how disturbance generated by sea otters (Enhydra lutris) digging for infaunal prey in eelgrass (Zostera marina) meadows increases genetic diversity by promoting conditions for sexual reproduction of plants. Eelgrass allelic richness and genotypic diversity were, respectively, 30 and 6% higher in areas where recovering sea otter populations had been established for 20 to 30 years than in areas where they had been present <10 years or absent >100 years. The influence of sea otter occupancy on the aforementioned measures of genetic diversity was stronger than those of depth, temperature, latitude, or meadow size. Our findings reveal an underappreciated evolutionary process by which megafauna may promote genetic diversity and ecological resilience.

Multiple Metrics of Temperature, Light, and Water Motion Drive Gradients in Eelgrass Productivity and Resilience

Characterizing the response of ecosystems to global climate change requires that multiple aspects of environmental change be considered simultaneously, however, it can be difficult to describe the relative importance of environmental metrics given their collinearity. Here, we present a novel framework for disentangling the complex ecological effects of environmental variability by documenting the emergent properties of eelgrass (Zostera marina) ecosystems across ∼225 km of the Atlantic Coast of Nova Scotia, Canada, representing gradients in temperature, light, sediment properties, and water motion, and evaluate the relative importance of different metrics characterizing these environmental conditions (e.g., means, extremes, variability on different time scales) for eelgrass bioindicators using lasso regression and commonality analysis. We found that eelgrass beds in areas that were warmer, shallower, and had low water motion had lower productivity and resilience relative to beds in deeper, cooler areas that were well flushed, and that higher temperatures lowered eelgrass tolerance to low-light conditions. There was significant variation in the importance of various metrics of temperature, light, and water motion across biological responses, demonstrating that different aspects of environmental change uniquely impact the cellular, physiological, and ecological processes underlying eelgrass productivity and resilience, and contribute synergistically to the observed ecosystem response. In particular, we identified the magnitude of temperature variability over daily and tidal cycles as an important determinant of eelgrass productivity. These results indicate that ecosystem responses are not fully resolved by analyses that only consider changes in mean conditions, and that the removal of collinear variables prior to analyses relating environmental metrics to biological change reduces the potential to detect important environmental effects. The framework we present can help to identify the conditions that promote high ecosystem function and resilience, which is necessary to inform nearshore conservation and management practices under global climate change.

Century-long records reveal shifting challenges to seagrass recovery.

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere. We show that meadows in the Western Baltic Sea exhibited major declines relative to historic (1890-1910) reference due to the wasting disease in the 1930s followed by eutrophication peaking in the 1980s, but have only shown modest improvement despite major eutrophication mitigation, halving nitrogen input since the 1980s. Across the past century, we identified generally shallower colonization depths of eelgrass for a given submarine light penetration and, hence, increased apparent light requirements. This suggests that eelgrass recovery is limited by additional stressors. Our study indicates that bottom trawling and intense recent warming (0.5°C per decade, 1985-2018), which impact on deeper and shallower meadows, respectively, suppress eelgrass from fully recovering from eutrophication. Warming is most severe in shallow turbid waters, while clear-water areas offer eelgrass refugia from warming in deeper, cooler waters; but trawling can prevent eelgrass from reaching these refugia. Efforts to reduce nutrient input and thereby improve water clarity have been instrumental in avoiding a catastrophic loss of eelgrass ecosystems. However, local-scale future management must, in addition, reduce bottom trawling to facilitate eelgrass reaching deeper, cooler refugia, and increase resilience toward realized and further warming. Warming needs to be limited by meeting global climate change mitigation goals.

Habitat alteration by invasive European green crab (Carcinus maenas) causes eelgrass loss in British Columbia, Canada

Dominant, habitat-forming plant species, such as seagrasses, are key components of coastal ecosystems worldwide. Multiple stressors, including invasive species that directly alter, remove, or replace the foundation plant species, threaten these ecosystems. On the Atlantic coast of North America, ecosystem engineering by invasive European green crab (Carcinus maenas) has been linked to the loss of some eelgrass (Zostera marina) beds. However, the interaction of the same co-occurring species on the Pacific coast has not been investigated. We conducted an enclosure experiment in Barkley Sound, British Columbia, to determine if the engineering impacts of green crabs on Pacific eelgrass ecosystems mirror those previously identified on the Atlantic coast. Eelgrass shoot density declined rapidly over 4 weeks, with a 73–81% greater loss in enclosures with high crab density compared to the low-density and control treatments. The low ratio of eelgrass blades to rhizomes in the high-density treatment suggests that blade shredding, rather than bioturbation of whole plants, was the main mechanism of eelgrass loss. Eelgrass was detected in green crab stomach contents, consistent with observations from the Atlantic coast. Crab density did not have a detectable effect on the biomass or community composition of benthic fauna associated with eelgrass over the duration of the experiment. The eelgrass loss we observed was consistent with losses observed on the Atlantic coast, which raises management concerns on the Pacific coast, particularly in areas where green crabs co-occur with other coastal stressors and with ecologically and economically important species such as salmon.

Eelgrass pathogen Labyrinthula zosterae synthesizes essential fatty acids

Negative consequences of parasites and disease on hosts are usually better understood than their multifaceted ecosystem effects. The pathogen Labyrinthula zosterae (Lz) causes eelgrass wasting disease but has relatives that produce large quantities of nutritionally valuable long-chain polyunsaturated fatty acids (LCPUFA) such as docosahexaenoic acid (DHA). Here we quantify the fatty acids (FA) of Lz cultured on artificial media, eelgrass-based media, and eelgrass segments to investigate whether Lz may similarly produce LCPUFA. We also assess whether field-collected lesions show similar FA patterns to laboratory-inoculated eelgrass. We find that Lz produces DHA as its dominant FA along with other essential FA on both artificial and eelgrass-based media. DHA content was greater in both laboratory-inoculated and field-collected diseased eelgrass relative to their respective controls. If Lz's production scales in situ, it may present an unrecognized source of LCPUFA in eelgrass ecosystems.

Temperature and salinity sensitivity of respiration, grazing, and defecation rates in the estuarine eelgrass sea hare, Phyllaplysia taylori

Highly dynamic environments such as estuaries are home to organisms accustomed to wide fluctuations in environmental conditions. However, estuarine temperature and salinity conditions are expected to shift with climate change, potentially altering plant and animal physiology and consequently their ecological interactions. Phyllaplysia taylori, a sea hare that lives exclusively in nearshore eelgrass beds in the Eastern Pacific Ocean, is a positive ecological interactor with eelgrass by increasing eelgrass productivity through grazing removal of photosynthesis-blocking epiphytes. The central aim of our study is to understand how increasing temperature and salinity are likely to alter that ecological interaction. First, we determined salinity thresholds for survival of P. taylori at 20 °C (typical summer temperature) for 2 weeks, and found that significant mortality occurs at salinity below 25 ppt. Then, we determined respiration rate, grazing rate, and defecation rate of P. taylori following a crossed 2-week acclimation at typical summer low- and high temperatures (18 and 22 °C) and salinities (27 and 33 ppt). P. taylori respiration and grazing rates were elevated under low salinity and high temperature. To determine how P. taylori responds to very warm and extreme summer temperatures, we measured respiration rates at higher temperatures (26 °C—very warm summer and 30 °C—heat shock) and feeding rates following exposure to the 30 °C heat shock. Irrespective of acclimation salinity, P. taylori acclimated to 18 °C were more sensitive to heat shock, as they had a larger increase in respiration rate at 30 °C, and had reduced feeding rates following the 30 °C exposure, whereas there was no reduction in feeding rate in 22 °C acclimated specimens. This study provides the first data on the salinity and temperature sensitivity and metabolic physiology of P. taylori with relevance to their trophic position in the context of eelgrass ecosystems.

Evidence for regional‐scale controls on eelgrass (Zostera marina) and mesograzer community structure in upwelling‐influenced estuaries

AbstractCommunity structure and function in ecosystems are dependent on top‐down and bottom‐up factors, which vary across local, regional, and temporal scales. In estuaries of the U.S. Pacific Northwest coast, eelgrass (Zostera marina) ecosystems are exposed to latitudinally varying oceanographic inputs in the form of ocean upwelling. Previous research suggests that ocean upwelling is critical to eelgrass and ulvoid macroalgae abundance, but the degree to which secondary producers are controlled by processes at regional vs. local scales is unknown. Here, we consider the relationships among primary producers (eelgrass, ulvoid macroalgae, and epiphytic microalgae), epifaunal mesograzers, and mesopredator fish within and across three Oregon, U.S.A., estuaries during a spring–summer season to examine the role of multiple scales in structuring these communities. Our objectives were to determine the relative importance of local and regional scales in organizing eelgrass communities and the potential of regional oceanography and trophic interactions in regulating patterns of primary producers in this system. We found that regional and seasonal patterns strongly influenced eelgrass community structure, providing support for the hypothesis that regional bottom‐up forcing predominantly controls these assemblages. Additionally, local effects were important to the patterns of primary producers, mesograzers, and mesopredator fish at specific sites, suggesting limited top–down control. Regarding management and conservation, the implications of our results are that in these highly productive systems, the potential for consumers to moderate the effects of eutrophication may be limited.

The effects of small-scale coastal development on the eelgrass (Zostera marina L.) distribution along the Swedish west coast – Ecological impact and legal challenges

Anthropogenic impacts on coastal areas have led to an increased degradation of marine environments globally. Eelgrass ecosystems are particularly susceptible to human induced stressors as they are sensitive to low light conditions and usually grow in shallow protected areas where pressure from coastal development is high. The extensive decline in coverage of eelgrass along the Swedish Northwest coast since the 1980s has largely been attributed to the effects of coastal eutrophication and overfishing. However, the impact on eelgrass from small-scale coastal development (docks and marinas) has never been investigated in this area. The aim of this study was to assess the local and large-scale effect of shading by docks and marinas on eelgrass habitats along the Swedish NW coast and to investigate the decision process behind small-scale exploitation to identify problems with the current legislation, which allows for continued exploitation of eelgrass. Through field assessments of eelgrass around docks and analysis of available data on eelgrass and dock distribution along the coast, the present study demonstrates that shading from docks reduced eelgrass coverage with on average 42–64% under and adjacent to the docks, and that floating docks affected larger areas and caused a much stronger reduction in eelgrass coverage (up to 100% loss) compared to docks elevated on poles (up to 70% reduction in coverage). The total eelgrass area negatively affected by docks and marinas along the NW coast was estimated to approximately 480 ha, an area corresponding to over 7% of the present areal coverage of eelgrass in the region. The analysis of decisions for dock construction showed that eelgrass was generally not assessed or considered in the decision process and that 69–88% of the applications were approved also in areas where eelgrass was present. Furthermore, marine protected areas only marginally reduced the approval of applications in eelgrass habitats. The continued small-scale development along the Swedish NW coast constitutes a significant threat to the already decimated coverage of eelgrass along the coast and changes in the management practices are needed in order to achieve both national and international goals on environmental status.

Large-Scale Differences in Community Structure and Ecosystem Services of Eelgrass (Zostera marina) Beds Across Three Regions in Eastern Canada

Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds.

Main Ecological Features of Benthic Macrofauna in Mediterranean and Atlantic Intertidal Eelgrass Beds: A Comparative Study

Main Ecological Features of Benthic Macrofauna in Mediterranean and Atlantic Intertidal Eelgrass Beds: A Comparative Study The present study compares the intertidal eelgrass macrofauna in two geographically and ecologically disparate localities (central Mediterranean and eastern Atlantic). Both coastal ecosystems are developed on extensive large mudflats with eelgrass beds, hosting a great diversity of water birds and providing important socio-economic assets. These two distinct and distant geographical ecosystems are affected by numerous anthropogenic pressures. By reflecting the response of the structure and functioning of benthic communities to climate change, the two eelgrass ecosystems provide a natural laboratory to investigate global warming. The macrobenthic fauna community of Zostera (Zosterella) noltei eelgrass beds was studied by sampling 34 stations in the Kneiss Islands and 48 stations in Arcachon Bay. A total of 148 species are identified in the Kneiss islands and 117 species in Arcachon Bay, but only 23 species are common to both ecosystems. Diversity, abundance and community structure are significantly different between the two study areas, which could be explained by differences between Mediterranean and Atlantic climatic conditions and by anthropic factors (e.g. fishing pressure, pollution, nutrient inputs) affecting each ecosystem. Multidimensional scaling (n-MDS) analysis identifies two distinct geographical station groups on the basis of species and familylevel abundance. On the contrary, three assemblages are identified on the basis of trophic groups distributed between the separate ecosystems. In terms of ecological quality status, the Kneiss site appears to have a good ecological condition and hosts a variety of sensitive species. On the other hand, biotic indices indicate that the Arcachon site is moderately perturbed and that the benthic communities are unbalanced. It is expected that the present-day functioning of the Kneiss Islands ecosystem will become typical of the situation in Arcachon Bay in several decades time, with the development of warmer and drier conditions.

Characterization of Ecosystem Structure within Transplanted and Natural Eelgrass (Zostera marina) Beds

Seagrass ecosystems are some of the most productive coastal habitats in the world. Eelgrass (Zostera marina) is an ecosystem engineer that provides important ecosystem functions and services. In 2010, the National Oceanic and Atmospheric Administration (NOAA) began construction of their Marine Operations Center-Pacific (MOC-P) in Yaquina Bay, Oregon; coupled with this were unavoidable habitat damages, and mitigation included the creation of a transplanted eelgrass bed. The purpose of this project was to assess the recovery of ecosystem structure and function within this transplanted bed using an ecosystem-based approach. Ecological indicators (e.g., eelgrass percent cover, faunal richness and abundance) and environmental variables (e.g., sediment and water quality parameters) were monitored over 12 months at the transplanted mitigation site and two reference sites. Each bed was observed to be unique in structure, predominately driven by physical setting. Eelgrass cover at the mitigation site remained unchanged and significantly lower than at reference sites; however, most faunal indicators within the transplanted eelgrass bed were comparable to those of existing eelgrass beds. During the first year post-transplant, the eelgrass bed within the NOAA MOC-P mitigation site remained stable and was observed to be adequately performing the functions associated with eelgrass ecosystems in the Pacific Northwest. Characterizing the transplanted bed with an ecosystem-based approach allowed us to accurately assess the site's progress toward mitigation goals and provide information important to management of the NOAA MOC-P mitigation site and future eelgrass mitigation efforts.

Reversal of intraspecific interactions by an ecosystem engineer leads to variable seedling success along a stress gradient

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 543:163-171 (2016) - DOI: https://doi.org/10.3354/meps11561 Reversal of intraspecific interactions by an ecosystem engineer leads to variable seedling success along a stress gradient S. Yang1,2,*, J. HilleRisLambers1, J. L. Ruesink1 1Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA 2Present address: Shannon Point Marine Center, Western Washington University, 1900 Shannon Point Road, Anacortes, WA 98221, USA *Corresponding author: sylvia.yang@wwu.edu ABSTRACT: By definition, ecosystem engineers can have large effects on resource flows and habitat structure, with impacts on other organisms ranging from facilitative to inhibitory. The stress gradient hypothesis posits that facilitative interactions predominate in conditions of environmental stress and switch to competitive interactions in benign environments. We conducted an empirical test of the stress gradient hypothesis for a marine ecosystem engineer, eelgrass Zostera marina L., across a hydrodynamic gradient. Eelgrass meadows perform important functions in coastal ecosystems and have experienced contemporary declines worldwide with variable recruitment success. In this study, we first determine whether eelgrass modified the local hydrodynamic conditions and then how the presence of an adult eelgrass canopy affected the plants’ own relative seedling success over the hydrodynamic gradient. Eelgrass reduced water motion significantly, which provided a positive feedback on survival and growth for conspecific seedlings, but only at the stressful end of the hydrodynamic gradient. By contrast, adult conspecifics negatively impacted seedling recruitment and growth in calmer environments, presumably due to intraspecific competition. Thus, eelgrass ecosystem engineering does not always facilitate the plant’s own performance, and our results support the stress gradient hypothesis as an explanation for this context dependence. The balance of these complex interactions may provide a mechanism for delayed or failed recovery of eelgrass in habitats exposed to high hydrodynamic exposure. KEY WORDS: Context dependence · Density dependence · Habitat modification · Seagrass · Stress gradient hypothesis Full text in pdf format PreviousNextCite this article as: Yang S, HilleRisLambers J, Ruesink JL (2016) Reversal of intraspecific interactions by an ecosystem engineer leads to variable seedling success along a stress gradient. Mar Ecol Prog Ser 543:163-171. https://doi.org/10.3354/meps11561 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 543. Online publication date: February 03, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Valuing Multiple Eelgrass Ecosystem Services in Sweden: Fish Production and Uptake of Carbon and Nitrogen

Valuing nature’s benefits in monetary terms is necessary for policy-makers facing trade-offs in how to spend limited financial resources on environmental protection. We provide information to assess trade-offs associated with the management of seagrass beds, which provide a number of ecosystem services, but are presently impacted by many stressors. We develop an interdisciplinary framework for valuing multiple ecosystem services and apply it to the case of eelgrass (Zostera marina), a dominant seagrass species in the northern hemisphere. We identify and quantify links between three eelgrass functions (habitat for fish, carbon and nitrogen uptake) and economic goods in Sweden, quantify these using ecological endpoints, estimate the marginal average value of the impact of losing one hectare of eelgrass along the Swedish northwest coast on welfare in monetary terms, and aggregate these values while considering double-counting. Over a 20 to 50 year period we find that compared to unvegetated habitats, a hectare of eelgrass, including the organic material accumulated in the sediment, produces an additional 626 kg cod fishes and 7,535 wrasse individuals and sequesters 98.6 ton carbon and 466 kg nitrogen. We value the flow of future benefits associated with commercial fishing, avoided climate change damages, and reduced eutrophication at 170,000 SEK in 2014 (20,700 US$) or 11,000 SEK (1,300 US$) annualized at 4%. Fish production, which is the most commonly valued ecosystem service in the seagrass literature, only represented 25% of the total value whereas a conservative estimate of nitrogen regulation constituted 46%, suggesting that most seagrass beds are undervalued. Comparing these values with historic losses of eelgrass we show that the Swedish northwest coast has suffered a substantial reduction in fish production and mineral regulation. Future work should improve the understanding of the geographic scale of eelgrass functions, how local variables affect the value of these functions, and how to defensibly aggregate a multitude of economic values.

Biodiversity mediates top-down control in eelgrass ecosystems: a global comparative-experimental approach.

Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.

Eelgrass Detritus as a Food Source for the Sea Cucumber Apostichopus japonicus Selenka (Echinidermata: Holothuroidea) in Coastal Waters of North China: An Experimental Study in Flow-Through Systems

Eelgrass ecosystems have a wide variety of ecological functions in which living tissues and detritus may be a food source for many marine animals. In this study, we conducted a laboratory simulating experiment to understand the trophic relationship between the eelgrass Zostera marina L and the sea cucumber Apostichopus japonicus. A mixture of decaying eelgrass debris and seafloor surface muddy sediments was used as food to feed A. japonicus, and then specific growth rates (SGR) and fecal production rates (FPR) were measured. According to the proportion of eelgrass debris, we designed five treatment diets, i.e., ES0, ES10, ES20, ES40, and ES100, with eelgrass debris accounting for 0%, 10%, 20%, 40%, and 100% in dry weight, respectively. Results showed that diet composition had a great influence on the growth of A. japonicus. Sea cucumbers could use decaying eelgrass debris as their food source; and when the organic content of a mixture of eelgrass debris and sediment was 19.6% (ES40), a relatively high SGR (1.54%·d−1) and FPR (1.31 g·ind.−1 d−1) of A. japonicus were obtained. It is suggested that eelgrass beds can not only provide habitat for the sea cucumber A. japonicus but can also provide an indirect food source for the deposit feeder. This means that the restoration and reconstruction of eelgrass beds, especially in coastal waters of China, would be a potential and effective measure for sea-cucumber fisheries, in respect to both resource restoration and aquaculture of this valuable species.